A conventional listening device such as a hearing aid includes, among other things, a microphone, an amplifier, and a receiver. The microphone receives an acoustic signal (i.e., sound waves) from the surrounding environment and converts the acoustic signal into an electrical signal. The electrical signal is then processed (e.g., amplified) by the amplifier and provided to the receiver. The receiver converts the processed electrical signal back into an acoustic signal and subsequently broadcast the acoustic signal to the eardrum.
A receiver for a conventional listening device is shown in FIG. 1. As can be seen, the receiver 100 includes a housing 102 that protects the sensitive components mounted inside the receiver 100. The housing 102 may be of a size and shape that allows the receiver 100 to be used in miniature listening devices, such as hearing aids. Within the housing 102 is mounted an electromagnetic drive assembly 104 that converts electrical signals from a microphone into acoustic signals. The electromagnetic drive assembly 104 includes, among other things, an armature 108 and an electrically conductive coil 110 through which the electrical signals from the microphone pass. Lead wires (not visible here) from the coil 110 extend through an opening in the housing 102 and terminate at a terminal 111 (e.g., a solder bump) on the outside of the receiver 100.
A magnet assembly 114 is also included in the electromagnetic drive assembly 104 adjacent to the coil 110. The magnet assembly 114 has a magnet housing composed of a pair of housing elements 116a and 116b. The housing elements 116a and 116b hold a pair of magnets (not visible here) that define a magnetic gap through which the working portion of the armature 108 extends.
In operation, an electrical signal passing through the coil 110 induces a magnetic field around the armature 108. Variations in the electrical signal produces fluctuations in the magnetic field, causing the armature 108 to alternate between moving toward one or the other of the magnets. A diaphragm 118 converts the armature movements, via a drive pin (not visible here), into a corresponding acoustic signal that is then broadcast to the eardrum.
The armature 108 is E-shaped, for example, with a base from which three parallel legs extend. Mounting of the armature 108 is such that the middle leg or reed of the armature passes through the center of the coil 110 along a central axis thereof, while the outer legs extend along the outside of the coil 110. The ends of the armature legs are then attached to the magnet assembly 114, which is adjacent to the coil 110.
Coil formation typically involves winding a conductive wire around a coil former. A coil winding bobbin may also be used to form the coil. Epoxy is usually applied to the coil to prevent corrosion. The coil former or coil winding bobbin is then removed using tweezers or other similar instruments. For an example of a coil winding bobbin that is removed, see European patent EP1219135B1. Removal of the coil former or coil winding bobbin, however, often produces inadvertent contact between the tweezers and the coil. This contact may cause damage to the epoxy, which can result in corrosion of the coil.
One solution to the above problem is to form the coil around a bobbin that is not removed. The middle armature leg or reed is then passed through the center of the bobbin and the outer legs extend along the outside. This solution, however, is lessened by the fact that it is usually very difficult to precisely center the middle armature leg within the bobbin. As a result, the inner height of the bobbin is typically made much larger than what is actually needed to accommodate the normal vibration of the armature leg.
Moreover, the armature 108 in the conventional receiver 100 is supported only at the ends of the legs where they are attached to the magnet assembly 114. The rest of the armature 108 is unsupported. As a result, large deflections may occur on the armature 108 when the receiver 100 is subjected to shock. A sufficiently severe shock may cause the armature 108 to deflect beyond the point of elastic deformation, thereby compromising the operation of the receiver 100.
Accordingly, what is needed is a receiver that is capable of inhibiting the large armature deflections that usually accompany a shock, and that is also capable of centering an armature leg within the coil of the receiver.